I am currently using a HP MediaSmart and have PyTivo and kmttg running on it. However it is getting old and I just had a drive failure on it. I can't get new drives and it is no longer being supported by HP. I'm looking to see what I can replace it with.

What I am currently using my server for:
PyTivo and kmttg
File server with user permissions from several PCs
Internet access to files on server
PC backups and recovery

I've looked at ReadyNAS and WD MyCloud.

My biggest concerns are PC backup and the ability to run other apps like PyTivo, since they seem to all have custom operating systems.

What do people suggest?
What are the plusses and minuses?
How are they different from the MediaSmart?
Would it be better to change to using Plex?